1. Field of the Invention
The present invention relates to oil and gas well drilling systems. More particularly, the present invention relates to fluid valves used to regulate or control fluid flows and pressures in a downhole environment. In one aspect, the present invention relates to an equalization valve used for sealing high differential pressure in a drilling environment during ancillary drilling operations.
2. Background of the Invention
During the drilling and completion of oil and gas wells, the downhole environment tends to be harsh and unforgiving. These harsh conditions include vibration and torque from the drill bit, exposure to drilling mud, drilled cuttings, and formation fluids, hydraulic forces of the circulating drilling mud, and scraping of sensitive equipment against the sides of the wellbore. Extreme pressures and temperatures are also present. Such harsh conditions can damage and degrade portions of the drill string, especially the equipment found in various tool strings.
Generally the drilling fluid flow is downward through the inner flow bore of the drill string, out through the drill bit, and back up through the annulus formed between the drill string and the borehole wall. However, often times it is required that the fluid flow, or portions thereof, be diverted, whether the fluid flow is found in the inner flow bore or in the annulus. For example, portions of the fluid flow may be diverted to provide hydraulic power to an independent system within the drill string, such as a packer module, to maintain continuous circulation of the drilling mud when primary drilling operations have been temporarily stopped, or to create or equalize a pressure drop between certain zones in the downhole environment. To achieve diversion of the fluid flow, particularly the fluid flow in the annulus, various valves have been developed.
Valves used in drilling operations are inherently susceptible to the harsh downhole conditions because they require the use of seals and moving parts. Valves that interact with the drilling mud flow are especially susceptible to the drilling mud, the deleterious debris carried by the drilling mud, and significant pressure drops. Unlike valves contained in closed systems, which typically interact only with a clean hydraulic oil, valves that interact with well fluids, called “dirty” fluid valves, are necessarily exposed to greater wear and degradation. The debris contained in well fluids tend to damage traditional valves using elastomeric seals. Thus, dirty fluid valves must be designed differently in order to compensate for their exposure to the debris in well fluids.
Often dirty fluid valves are exposed to the drilling environment because they are needed to create or diffuse a differential pressure between the drilling environment and some system that has been closed off from the drilling environment. This type of valve is typically called an equalizer valve. The function of the equalizer valve is to either isolate or connect the annulus of the borehole with a flowline of the valve internal to the drill string. When the annulus is isolated from the internal flowline, a significant pressure drop is created on the order of thousands of psi's. If the default position of the valve is to connect the annulus with the internal flowline, then the valve is considered normally open. If the default position is isolation, then the valve is considered normally closed.
Because the pressure differential is so great when the annulus is isolated from the internal flowlines of the drill string, valve and other seals are susceptible to blow-out and rapid degradation. Thus, equalizer valves are used to balance the pressure differentials. In order to reduce the wear on the seals, these valves are often normally open-type valves (connecting the annulus with internal flowlines). Despite being normally open, equalizer valves remain inherently susceptible to the abrasive nature of the well fluids that the valves interact with. Thus, the industry would welcome a reliable, normally open, dirty fluid valve for sealing high differential pressure in a drilling environment which is also field replaceable without disturbing the hydraulics circuit or other structure used to actuate the valve.